fix: silence errors only on test command

What

fix: silence errors only on test command

The SilenceUsage and SilenceErrors was applied to all commands thus making commands like jsonnet-tool yaml not printing out any errors as it used to.

The flag was added in !122 (merged)

Why

Latest version of jsonnet-tool:

❯ echo 'this should error' > rule.jsonnet
❯ jsonnet-tool yaml rule.jsonnet

In this MR:

❯ echo 'this should error' > rule.jsonnet
❯ ./jsonnet-tool yaml rule.jsonnet
Error: failed to evaluate jsonnet: rule.jsonnet:1:6-12 Did not expect: (IDENTIFIER, "should")

this should error

: command failed
Usage:
  jsonnet-tool yaml [flags]

Flags:
  -C, --ext-code stringToString     Provide an external value as a Jsonnet code to jsonnet (default [])
  -V, --ext-str stringToString      Provide an external value as a string to jsonnet (default [])
  -H, --header string               Write header to each file
  -h, --help                        help for yaml
  -J, --jpath stringArray           Specify an additional library search dir
  -m, --multi string                Write multiple files to the directory, list files on stdout (default ".")
  -p, --prefix string               Prefix to append to every emitted file
  -P, --priority-keys stringArray   Order these keys first in YAML output